1. Field of the Invention
The invention relates to determining flight parameters of the aircraft, or to other science and technology fields where fluid and gas flows are involved.
2. Description of the Related Art
Measurement of flow parameters is one of the most important concerns of atmospheric flight mechanics and aerodynamics of the aircraft. Presently, for measuring of flight (flow) parameters used are air-pressure heads (APH) frequently mounted directly on aircraft fuselage or any other component thereof, which heads measure actual parameters of a local flow approximating a planar flow. The aircraft are generally fitted with a plurality of such APH""s that measure local parameters of a flow. True flight parameters are determined on the basis of calibrations carried out beforehand. Measuring of flight parameters is a very important task for high-maneuverability airplanes in view of the substantially broadened in-flight angles of attack and a wide range of flight speeds (from slow subsonic speeds to those that far exceed the supersonic speed). This task is rather important for helicopters in connection with their high maneuvering capabilities (i.e., forward or backward, to the right or left, upward or downward flights) and automation of these flight modes using the data obtained from a flight parameter measurement system.
Known is an air-pressure head, comprising a housing in the form of a round cylindrical rod having intake orifices arranged around the cross-section circumference and connected via ducts to nipples (Petounin A. N., Metodyxe2x80x94Techniques and Equipment for Measuring the Gas Flow Parameters), M., Machinostroyeniye publishers, 1972, pp. 88-100, FIG. 1.102; Glaznev V. N., Zavaroukhin S. G., Experimental Investigation of Planar and Axially Symmetrical Vortex Flows using a Cylindrical Sensor in a Wide Numeric Range, M., Proceeding of Central Institute for Aerohydrodynamics, vol. 14, N 4, 1983). Flow parameters are determined using said head by measuring the pressures occurring at the windward side of the head in the area of continuous flow according to the calibration relationships that enlink the determined parameters with the measured pressures.
The disadvantages of the APH of the above-discussed type are as follows:
the impossibility of measuring static pressure to an acceptable accuracy in the range of M values from 0.8 to 1.1 due to the known phenomenon of the transonic stabilization;
the impossibility of using, for determining the flow parameters, the inlet orifices disposed at the leeward side in the head""s separating flow zone, in which orifices the pressures, though not being subjected to the transonic stabilization effect, strongly depend on Reynolds number, roughness of the surface and turbulence level of the incoming flow;
still another disadvantage, being actually a result of the preceding disadvantage, consists of a significantly excessive number of pressure measuring ducts. For determining three parameters (total pressure P1, static pressure Ps and downwash angle xcex1) this APH requires such to be provided with at least three orifices at the windward side in the separation-free zone. Rough estimates demonstrate that when the flow parameters are to be determined within the range of xcex1=0÷360xc2x0. For acceptable sensitivity being maintained, at least 8 to 9 inlet orifices, that are equally spaced (the pitch being 45xc2x0 or 40xc2x0) around the APH cross-section circumference, are required, which results in greater dimensions of an APH, its increased aerodynamic drag, greater weight of structure of an APH itself and also that of measuring instruments, because a pressure sensor must be connected to each of the ducts. Further, this results in a more expensive measuring system based on such APH""s.
Known is a device (Europaische Patentschrift, Veroffentlichungsnummer, 0049756 B1, G 01 F 1/46, G 01 L 13/00, Vorrichtung zum Messen des Differenzdruckes; prioritaet: 09.10.80 DE 3038180, Patentinhaber; IWK Regier and Kompensatoren GmbH: Erfinder: Fehbr, Dieter, Dr., Dipl-Phys.) adapted to measure a pressure drop. The basic element of this device is a rod in the form of regular hexagonal prism having on one of its edges an orifice (or a plurality of orifices connected to pneumatic ducts) intended for pressure measuring. When the rod in a flow is oriented such that the flow velocity vector extends through the edge that has an opening, the rod axis and the opposite edge, the pressure approximating the total pressure is sensed using a pressure sensor connected via a pneumatic duct to said orifice(s). When the rod in a flow is oriented such that the orifices thereon are deployed with respect to the velocity vector at 180xc2x0, the base pressure can be determined using these orifices. Thus, using APH""s of this type, the flow strength (or total Pt and static Ps pressures) can be measured on the basis of the preset calibrations. Said patent proposes the devices consisting of two rods oriented as described above and intended to measure Pt and P2 is gas conduits.
However, such APH, or a device based thereon, are not suitable intrinsically to measure three flow parameters at a time (total pressure Pt, static pressure Ps and angle of downwash (attack) xcex1) for it lacks the appropriate number of orifices, at least three orifices, for intake of pressures. Actually, the flow parameters are known to be determined on the basis of predetermined relationships between pressures Pi and angle of attack (downwash) xcex1 of an undisturbed flow, total Pt and static Ps pressures of an undisturbed flow:
Pi=fi(xcex1, Pt, Ps),xe2x80x83xe2x80x83(1)
measured in an air-pressure head in i number of points of pressure intake. For resolving this system of equations with respect to xcex1, Pt, Ps, it is required to have ixe2x89xa63 orifices, and, further, such system of equations must be sufficiently well-posed. For example, when two orifices i=1 and i=2 are located in the separation zone where the pressure is equalized, then P1≈P2 will be effective in a broad range of xcex1xe2x80x2, and the system becomes ill-posed or unresolvable. Hence, when it is required to measure parameters of a plane-parallel stream within the range of xcex1=0÷360xc2x0, the APH body must have, as the analysis of the experimental data demonstrates, ixe2x89xa64 orifices, and they are to be distributed such that to perform  less than  less than switching greater than  greater than  from some orifices to another ones.
Another disadvantage of the mentioned prior art is the circumstance that the pressure intake orifices are disposed on a prism edge. This results in that even in a slight re-orienting of such APH relative to the flow (the position as discussed above), a flow separates from that edge. This results in a loss of sensitivity to a change in xcex1, i.e. said system of equations (1) becomes unresolvable.
The most pertinent art is an air-pressure head implemented in the form of a rod having cross-section of equilateral triangle. On the rod end face, on the axis common with said rod, positioned is a cylindrical superstructure having cross-section in the form of equilateral triangle whose sides are equal to those of the rod cross-section, said triangle being slewed with respect to the rod cross-section by angle xcfx86=60xc2x0. On facets of the rod and superstructure, implemented are six inlet orifices connected via ducts to nipples (Golovkin M. A., Yefremov A. A., Priyomnik vozdoushnogo davleniya, [An Air-Pressure Head], Patent of the RF N 1809341, priority as of Apr. 8, 1991).
The disadvantages of that APH are as follows:
complexity of design;
insufficient accuracy in determining flight parameters, particularly in case of sliding;
an excessive number of pressure-measurement ducts, which circumstance results in a greater weight of an APH itself and a measuring system as a whole.
The object of the invention is to simplify the design, to improve the accuracy of measurement of flight (flow) parameters, and to reduce the APH structure weight and that of a measuring system as a whole.
The contemplated technical results is to be attained with the following technical solution: an air-pressure head is implemented in the form of a multiple-edge rod, whose edges are oriented along the rod axis, having groups of orifices disposed between the edges on smooth lateral surfaces of the rod and connected via pneumatic ducts to outlet nipples disposed off the flow. The edges in the longitudinal direction are continuous and their number is nxe2x89xa63; groups of orifices are spaced from the edges that define the lateral surface at the value of a xe2x89xa60.1 b, where b is the distance between the edges in any cross-section of the rod; the angle between the lateral surfaces in any cross-section of the rod being xcex3 less than 180xc2x0. Thereby the design is simplified and the accuracy of determining of flight parameters in case of sliding is also improved owing to the absence of the tearing-off wake that is outgoing in case of the APH of the most pertinent art from the place of joint of its two parts (the rod and superstructure) and approaching the inlet orifices.
The contemplated technical results is also to be attained using the following arrangement: sharp edges can be rounded or rendered obtuse by chambering, said rounding or chamfer being conjugated with smooth lateral surfaces of the rod at the distance of cxe2x89xa60.005b from the place of conjugation of two contiguous lateral surfaces. Such rounding or chamber can be of the merely technological nature. Said value of cxe2x89xa60.05b, according to the experimental investigation findings, actually provides referencing of the flow separation line to the area of conjugation of rounding or chamber to the rod lateral surfaces, whereby independence of measurements from the Reynolds number is ensured. The contemplated technical result is also to be achieved through that the edges are made in the form of protrusions of the rod having height of hxe2x89xa60.1 b and being exe2x89xa60.1 b wide, as measured in the rod cross-section. Such shape of said protrusions, provides, as the carried-out experimental investigation demonstrates, referencing of the flow separation line to a protrusion, and also provides independence of measurements from Reynolds number. In certain cases a protrusion-shaped edge is capable of simplifying the design to a considerable extent.
The contemplated technical results is also to be attained through that the rod lateral surface is cylindrical or tapered. Thereby the design is simplified and manufacture thereof becomes less expensive.
The contemplated technical result is also to be attained through that the rod lateral surface between the edges is convex. Such shape of the APH rod allows, on one hand, to minimize influence of Reynolds number in respect of pressure measuring, and, on the other hand, to improve the instrument sensitivity owing to growth of derivative of measured pressures with respect to the downwash angle, which results in a substantial decrease of number of instrumental errors which occur.
The contemplated technical result is also to be attained through the fact that the number of edges on the rod is selected to be four, five or six edges, depending on the needed range of angles of attack, wherein the flight (flow) parameters are to be measured. In particular, when measurements are to be done within the range of xe2x88x9290xc2x0 less than xcex1 less than 90xc2x0, as the carried-out trails demonstrate, it will be sufficient to use a four-edge rod, because on a rod two pressures (e.g., P1 and P2), being sufficiently sensitive to changes in xcex1, Pt, Ps, at the APH windward side can always be selected, and one pressure (P3) can be taken at the leeward, base side of an APH. Then, as the carried-out experiments demonstrate, said system of equations (1) is resolvable with respect to xcex1, Pt, Ps, and thereby the required number of the pressure measurement ducts could be reduced with the effect of a reduced weight of an APH itself and a measuring system as a whole. When the required range of angles of attack is xcex1=0÷360xc2x0, wherein the flight (flow) parameters are to be measured, as the experiment findings demonstrates, either the five- or six-edge rod has to be used.